Servo-control systems are known and used throughout a number of industries where accurate, motor-controlled movement is required. One such servo-control system is illustrated in FIG. 1.
As illustrated, the servo-control system, shown generally at 10, includes a programmable control system 20 having an output along one or more lines 30 to control a servo-amplifier 40. The servo-amplifier 40, in turn, is connected to control a servomotor 50 along one or more lines 60. Execution of a predetermined motion profile that is stored in the programmable control system 20 may be initiated by start switch 70. Upon detection of a depression of the start switch 70, the programmable control system 20 sends the necessary control signals along lines 30 to the servo-amplifier 40 which drives the servomotor 50 in accordance with the received control signals to implement the motion profile.
As the motion profile is being executed, it may be necessary to stop the movement of the servomotor 50, for example, in an emergency, to prevent injury. Accordingly, an emergency stop switch 80 may be used to indicate to the programmable control system 20 that there is a need to stop the motion of the servomotor 50. Upon detection of the actuation of the emergency stop switch 80 by the programmable control system 10, the programmable control system 10 sends the appropriate commands to the servo-amplifier 40 to cease further motion of the servomotor 50.
One potential problem with the foregoing system is that it fails to recognize the potential for a failure of the programmable control system 20 or the servo-amplifier 40. More particularly, it is possible for the programmable control system 20 to fail to detect the actuation of the emergency stop switch 80 and/or fail to send the appropriate braking signals to the servo-amplifier 40. Likewise, the servo-amplifier 40 may fail to properly receive and/or respond to the braking signals sent by the programmable control system 20 when the system 20 detects the actuation of the emergency stop switch 80. In either instance, the servomotor 50 may continue to operate in a situation in which operation must necessarily cease.